Joint bids of two cauntries are permitted(under exceptional circumstances joint bids by three member countries may also be considered). The bidding process will start in 2012.
The suggestion of minimum stadiums:
2 stadiums with 50,000 seats
3 stadiums with 40,000 seats
4 stadiums with 30,000 seats
The final bid requirements will be distributed in the second phase by UEFA in April 2013.
Expanded Format:
The format of the tournament will consist of six groups a four teams, followed by a round of 16, quarterfinals, semifinals and the final. The top two from each group would qualify in addition to the four best third-placed teams. This format would generate a total of 51 games, compared with 31 now, to be played over a period of ~30 days depending on the match schedule. This historic decision gives medium-ranked countries a much greater chance to qualify for the finals. The traditional qualifying structure, with groups of six or five teams, will remain in place.
Bids to date:
Seven candidates have made a bid to stage the UEFA Euro 2020:
Bosnia-Herzegovina / 
Croatia / 
Serbia 
Armenia / 
Azerbaijan / 
Georgia 
Bulgaria / 
Romania / 
Hungary 
Czech Republic / 
Slovakia
Netherlands
Belgium 
Turkey
Poland
Finland